The described embodiments relate to wireless communications devices, and more particularly, to systems, methods, apparatus, processors and computer readable media for determining the radiated performance of an antenna system associated with a wireless device.
Wireless devices utilize radio waves to provide long distance communications without the physical constraints of a wire-based system. The wireless device transmits and receives information using via the radio waves, which may be carried over predetermined frequency bands. An antenna connected to a transmitter and a receiver, along with the associated circuitry, allows the wireless device to transmit and receive these radio wave signals. The design of the wireless device, including the antenna and the various transmit- and receiver-related components, impact the ability of the wireless device to transmit and receive radio wave signals, and hence define and affect the radiated performance of the device. Thus, it is desirable to determine and tune the radiated performance of a wireless device to optimize the ability of the wireless device to communicate radio wave signals.
Prior art methods of determining the radiated performance of a wireless device, however, have a number of drawbacks. Some tests to determine radiated performance involve destructive modification of the wireless device. For instance, in one example, the signal path between the antenna and receiver is interrupted and re-routed to an external radio frequency (“RF”) connector. Radiated signal power measurements are then made by external test equipment interfaced at this connector, thereby acting as a substitute for the receiver on the wireless device. The presence of the external RF connector and the associated external cable can distort the true radiated performance of the wireless device. Further, these destructive modifications add expense to the testing procedure due to both the additional equipment and the additional manpower required to make the modification. Additionally, destructive modifications add further expense by making the modified wireless device un-usable for other tests.
Additionally, in a wireless communication system, an RF modulated signal from a transmitter may reach a receiver via a number of propagation paths. The characteristics of the propagation paths typically vary over time due to a number of factors such as fading and multipath.
Further, structures such as buildings, and surrounding terrain, including walls and hillsides, contribute to the scattering and reflection of the transmitted signal. The scattering and reflection of the transmit signal results in multiple signal paths from the transmitter to the receiver. The contributors to the multiple signal paths change as the receiver moves.
Other signal sources also result in degradation of the desired signal. The other signal sources may be other transmitters intentionally operating on the same frequency as the desired signal, as well as transmitters that generate spurious signals in the frequency band of the desired signal. Yet another source of signal degradation may be generated within the receiver itself. Signal amplifiers and signal processing stages within the receiver may degrade the level of the desired signal with respect to the level of thermal noise. The signal amplifiers and processors within the receiver may also generate noise products or distort the received signal and further degrade its quality.
To provide diversity against deleterious path effects and improve performance, multiple transmit and receive antennas may be used. If the propagation paths between the transmit and receive antennas are linearly independent (i.e., a transmission on one path is not formed as a linear combination of the transmissions on other paths), which is generally true to at least an extent, then the likelihood of correctly receiving a data transmission increases as the number of antennas increases. Thus, generally, diversity increases and performance improves as the number of transmit and receive antennas increases.
Further, a wireless device may use multiple antennas for a number of reasons. For example, a wireless device often needs to operate over multiple bands and service multiple operating modes. Another reason is that advanced transceiver architectures are being implemented that use multiple antennas for improving the performance of some of these modes in the field. When operated simultaneously, these modes can interfere with each other, causing degrading overall performance. So it is important to devise accurate means of evaluating the radiated performance of a wireless device that can capture the effects of self-interference. Current methods require several steps to evaluate a combined device/antenna design, and there is ambiguity with respect to test accuracy with current “cabled” tests. Therefore, dependable design and test methodologies have yet to be developed.
Thus, new and improved systems, apparatus, computer-readable media, processors and methods for determining the radiated performance of a wireless device are desired.